Glitches

Regenerate items

Chapter 2-1, take all the items at the beginning and then Quit the game. Return to the game by selecting "Continue" and you will begin Chapter 2-1 with the items you got before you quit the game, however, the items at the beginning (you took just now) are still at the same place, so you can obtain them again. Repeat the same thing to get as many as you like.

Note: This works on any stage, this is just one example of how to benefit from it.